Exemplary embodiments of the invention relate to a method for operating an internal combustion engine.
German patent publication DE 102 42 226 A1 discloses a method for forming an ignitable fuel-air mixture in a combustion chamber of a spark-ignition internal combustion engine with direct injection, in which combustion air is supplied to a combustion chamber via at least one intake duct. Fuel is injected into the combustion chamber by a fuel injector situated in the combustion chamber. A fuel-air mixture that is formed is ignited by at least one spark plug situated in the combustion chamber, the fuel injection taking place in multiple partial quantities. During homogeneous operation of the internal combustion engine the fuel injection is designed in such a way that a first and a second partial quantity are introduced in the intake stroke, and a third partial quantity is introduced in the compression stroke, the ignition of the fuel-air mixture that is formed taking place at a distance between 0° crankshaft angle and 100° crankshaft angle after the end of the injection of the third partial quantity.
In addition, during stratified charge operation of the internal combustion engine the fuel injection is designed in such a way that a first, a second, and a third partial quantity are introduced into the combustion chamber in a compression stroke of the internal combustion engine, the fuel injection of the second partial quantity being ended at a crankshaft angle in a range between 15° crankshaft angle prior to ignition of the formed fuel-air mixture and 4° crankshaft angle after the ignition of the formed fuel-air mixture.
German patent publication DE 10 2004 061 142 A1 discloses a method for controlling an internal combustion engine. The internal combustion engine has a device for switching over the effective valve lift curves of charge cycle valves, a throttle valve that is controllable by a control device, and at least one controllable injection element, the request for a switchover being recognized prior to switching over the valve lift curves, and the throttle valve position being predictively changed prior to switching over the valve lift curves. At least after the predictive correction of the throttle valve position triggered by the switchover request, the desired setpoint torque and the actual torque are continuously determined, and the switchover of the effective valve lift curve is delayed with respect to the switchover request, the switchover time being determined from the rate of deviation of the actual torque from the setpoint torque.
It has been shown that during operation of an internal combustion engine, in particular a gasoline engine, having relatively small valve lifts of at least one gas exchange valve, in particular an intake valve, associated with a combustion chamber of the internal combustion engine, disadvantages may result with regard to a charge movement of the fuel-air mixture in the combustion chamber compared to larger valve lifts.
Exemplary embodiments of the present invention, therefore, are directed to a method for operating an internal combustion engine in which the disadvantages of the charge movement are at least very small or avoided.
In such a method for operating an internal combustion engine of a motor vehicle, at least one injection of fuel directly into at least one combustion chamber of the internal combustion engine is carried out by means of at least one injection device. In addition, ignition of a mixture of the fuel and air in the combustion chamber is carried out by means of an ignition device.
The internal combustion engine is operated selectively in at least one first operating mode with at least one first valve lift of at least one gas exchange valve of the internal combustion engine, associated with the combustion chamber, or in at least one second operating mode with at least one second valve lift that is smaller than the first valve lift. In other words, the injection and the ignition are carried out in both operating modes, the gas exchange valve in the first operating mode performing the first valve lift, and in the second operating mode performing the second valve lift, when the gas exchange valve opens and closes. The second valve lift is smaller than the first valve lift.
To now compensate for disadvantages of a smaller charge movement of the mixture in the second operating mode, with the second valve lift, in comparison to the first operating mode with the first, larger valve lift, for assisting the charge movement in the second operating mode, at least one further injection of fuel directly into the combustion chamber is carried out prior to the ignition. On account of assisting the charge movement due to the further injection, slower combustion in the second operating mode compared to the first operating mode may also be avoided, resulting in efficient operation of the internal combustion engine with low fuel consumption and low CO2 emissions. The method according to the invention thus allows the provision of control times of the gas exchange valve or of at least one camshaft of the internal combustion engine that actuates the gas exchange valve, in the second operating mode, resulting in very low fuel consumption due to very low charge cycle work.
The further injection is preferably carried out close to the time of ignition. This results in particularly advantageous assistance of the charge movement, and thus, particularly advantageous turbulence of the mixture, in particular at the time of ignition, resulting in very high combustion stability. This is beneficial for the efficient operation of the internal combustion engine.
For providing very good charge movement, and thus, turbulence having a very good, beneficial effect on the combustion stability, it is preferably provided that the further injection is carried out after the at least one first injection.
In another advantageous embodiment of the invention, multi-spark ignition is carried out as the ignition, at least in the second operating mode. Particularly high combustion stability is thus achieved, resulting in very efficient operation of the internal combustion engine, which is designed, for example, as a reciprocating internal combustion engine.
In another advantageous embodiment, in the second operating mode the internal combustion engine is operated, at least for the most part, in homogeneous operation. In homogeneous operation, the mixture, in particular in comparison to a possible stratified charge operation of the internal combustion engine, is particularly homogeneous, thus enabling particularly efficient operation of the internal combustion engine.
The internal combustion engine may be operated, at least for the most part, in homogeneous operation in the first operating mode as well.
The fuel consumption and thus the CO2 emissions of the internal combustion engine may be kept low particularly when a load setting of the internal combustion engine in the second operating mode is carried out by means of at least one throttle valve situated in an intake tract of the internal combustion engine and/or by means of a supercharging rate of at least one exhaust gas turbocharger associated with the internal combustion engine and/or by means of a phase adjustment of the camshaft, i.e., by means of a change in the control times of the gas exchange valve, which is designed in particular as an intake valve.
In another advantageous embodiment, the internal combustion engine is operated in the second operating mode when at least one value which characterizes at least a temperature of the internal combustion engine exceeds a predefined threshold value. The threshold value is 50° C., for example. Efficient operation of the internal combustion engine with low fuel consumption may be ensured in this way.
The gas exchange valve is preferably an intake valve, in the at least one open position of which air may flow into the combustion chamber from an intake tract of the internal combustion engine.
Further advantages, features, and particulars of the invention result from the following description of one preferred exemplary embodiment, and with reference to the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and/or only shown in the figures may be used not only in the particular stated combination, but also in other combinations or alone without departing from the scope of the invention.